We propose to study the role of DNA-dependent RNA polymerase in gene regulation during the differentiation of bacteria into spores. We have suggested that changes in gene expression during sporulation may be in part regulated by changes in the template specificity and subunit structure of RNA polymerase. Early during sporulation of Bacillus subtilis there is a marked decrease in the activity of the sigma component of RNA polymerase. This decrease is accompanied by the appearance of at least one new polypeptide of 70,000 daltons that is apparently bound to RNA polymerase in sporulating cells. Our goal is to determine the mechanism by which sigma is inactivated during spore formation and to determine whether the 70,000 dalton protein and proteins associated with RNA polymerase direct the synthesis of sporulation messenger RNAs in vitro from B. subtilis DNA as a template.